Support duplicate timestamps by merging into single timestamp

[tylerdak]

Hey there!

I've noticed that ytdl-sub throws an error when duplicate timestamps are found in its check for ascending order. Makes total sense for albums where you only have one track at a time, but I've found user-submitted timestamps for DJ sets sometimes feature these. For example, the top timestamp comment under this video.

This pull request adds support for these duplicate timestamps by combining them into one with a delimiter in the timestamp title to split them up. I can change the delimiter if preferred, but it seemed like a good obvious one.

To find duplicates, I added a comparison to the last added Timestamp. If they match, the last added title is appended with the delimiter and the duplicate timestamp title. The duplicate's Timestamp object is ignored so only a single Chapter is created for that timecode.

Hoping we can get this implemented! Thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 91.79%. Comparing base (0ebcfb6) to head (d07b735).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1179   +/-   ##
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  Coverage   91.79%   91.79%           
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  Files         113      113           
  Lines        7445     7449    +4     
=======================================
+ Hits         6834     6838    +4     
  Misses        611      611           

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[jmbannon]

Thanks @tylerdak for the concise and tested change!